Vacuum tube



Nov. 22, 1927.

' E. L. CHAFFEE VACUUM TUBE Original Filed Oct. 14. 1918 2 Sheets-Sheet 1 INVENTUR HISUTORNEY Nov. 22, 1927.

E. L. CHAFFEE VACUUM TUBE Original Filed Oct. 14. 1918 2 Sheets-Sheet 2 V0 LTS 0N GRID I INVENTOR HIS ATTORNEY Patented Nov. 22, 1927.

UNITED STATES PATENT OFFICE.

EMORY LEON ORA-FREE, OF DELIGHT, MASSACHUSETTS, ASSIGNOB TO JOHN HAYS HAMMOND, J'B.,, OI GLOUCESTER, MASSACHUSETTS.

VACUUM TUBE.

Application filed October 14, 1918, Serial No. 257,993. Renewed February 27, 1925.

Some of the objects of the present invention are to provide in a radio receiving system improved means for reducing the d sturbing efiects of interference, or statue in such a manner that large variations of potential caused by large or intense signals will produce no greater efiect upon a telephone or other similar or suitable recelving instrument than would be produced by a comparatively weak signal; to provide an improved detector; and to provide other lmprovements as will appear hereinafter.

In the accompanying drawings, Fig. 1 represents a. diagrammatic side elevation of one form of a receiving system constructed in accordance with the present invention; Fig. 2 represents a sectional elevation of one form of detector embodying the present invention; Fig. 3 represents a side elevation of the detector; Fig. 4 represents a detail of a grid used in the detector; Fig. 5 represents a section on line 5-5 of Fig. 2; Fig. 6 represents a plate current curve of a detector plotted in conjunction with a grid current curve; Figs. 7 and 8 represent respectively characteristics of the ideal curve of sensitiveness of a detector of the bulb type; Figs. 9 and 10 represent curves plotted for difierent variations in the grid potential.

' 30 Referring to the drawings, one form of radio receiving system is shown in Fig. 1 wherein an open aerial circuit including an antenna 10, prima coil 11 and ground 12 is illustrated as coup ed with a closed oscillator circuit 13 including a secondary coil 14 an a variable condenser 15. One side of the condenser 15 is connected by a lead 16 to a grid 17 of a detector 18 while the opposite side of the condenser 15 is connected by a lead 20 through a potentiometer 21 and a suitable resistance 22 to a filament 23 of the detector 18. This filament 23 is maintained heated by a. battery 24 controlled by a rheostat 25. The detector 18 is arranged to control a receiving circuit 30, the terminal leads 31 and 32 oi which are respectively joined to the filament 23 and the plate electrode 33. The circuit includes a high potential buttery 34 and a telephone receiver 35 or any other suitable receiving instrument.

0 For the purpose of reducing the effect of intense signals upon the receiving circuit a form of detector is employed, preferably of the gaseous type, comprismg a bulb 36 of hme glass or any other suitable composition mounted in a. base 37 such as a brass cylindrical member filled with insulation 38 through which the. lead wires pass to the grid 17 filament 23 and the plate electrode In the form of detector here shown, the plate electrode 33 consists of a nickel cylinder suspended within the bulb 36 by means of suita le wires 40 fixed to a glass arm sup port 41 formed as a part of the bulb proper. The cylindrical plate electrode 33 encircles the grid structure which is here formed as an elongated coil 42 the convolutions of which are connected at a plurality of points by interwoven wire strands 43 arranged parallel to the longitudinal axis of the coil. The grid coil 17 is suspended by a wire 44 from the support 41 and encircles the filament 23, but is out of contact therewith. This detector, when pumped to a certain pressure indicated by the appearance of the dischar e from the nduction coil, such as a green uorescence on the lime glass walls of the bulb and a trace of: blue in the center of the bulb, acts to reduce the effect of intense signals and limits the possible variations of the plate or output current. In order to provide a detector bulb or tube which will give the desired results the particular characteristic curve which the detector should have is decided upon and then the tube or bulb constructed and pumped to give the required curve. It may then be operated at the proper point on the curve for the achievement of the desired result.

In order that this use of a characteristic 9U curve may be clear, reference is made to Fig. 6 of the drawings where a curve represents a typical plate current curve which might be possessed by a detector constructed in accordance with the invention and which is plotted 95 against volts on the grid as abscissas. A

curve 51 represents the corresponding grid current curve plotted to a current scale representing smaller currents than the scale for the plate current. It is well known that if the potential of the grid varies by a small increment V, both plus and minus about a constant polarizing potential A, the plate current will suffer an average increase because the curvature of the .plate curve is such about the point A that a greater increase than decrease in plate current is produced, when the potential varies by the same amount on either side of A. On the other hand, a variation of potential of the grid about the point B will produce an aggregate decrease in plate current. A curve S can then be plotted, the ordinate of which will represent the change in plate current caused by a certain variation of grid potential about the polarizing potential represented by the distance of the ordinate from the zero axis of volts. If the ordinate of sensitiveness is plotted upward it means that the plate current increases and if plotted in a negative direction the current decreases. At the points of maximum increase or decrease the maximum change of plate current occurs, which means that tector has its maximum sensitiveness. If a large potential variation of the grid occurs a greater change in plate current obtains, which is proportional to the area under the sensitiveness curve bounded b the limits of potential variation. It is evi ent, therefore, that a variation of potential above the point C will give no response. Should, however, the grid 17 be polarized to the potential represented by the point A, then any variation of potential of maximum amplitude less than A C will give a signal or response proportional to the area under the curve bounded by the two limits of potential on either side of A. It is apparent that the area does not increase in proportion to the increase in voltage, so that a loud or intense signal does not ve a response proportional to its intensity Elli the response is lessin proportion the more intense the signal.

If the potential variation exceeds the value A G, the area representing the response will extend over into the negative part of the S curve and this area must be subtracted from the positive area. Thus a potential variation eater than A C will actually produce al ae response than a small potential variation as ven' by A C.

In Fig. 7 a cm of sensitiveness curve of an ideal bulb is shown, wherein a potential variation about A reaching on either side of A to the points B and C will give the maximum variation of plate current obtainable and any variation of potential greater or less than that will give less response. In Fig. 8 another form of ideal sensitiveness curve is shown.

the device used as a de-' In the practical operation of a detector, the above ideal conditions may be approximated, for example by introducing a certain amount of gas, such as air at a pressure of of a millimeter into the evacuated bulb and designing the grid accordingly. Thus in Fig. 9 a typical sensitiveness curve is one plotted in accordance with one form of detector and closely approximates the ideal curve of Fig. 6 except that the curve is not sufiiciently compressed in the direction of grid volts that is, the range of grid volts 0 which the variation in the potential of the message should have to give the best protection against interference is greater than the potential of most radio signals. To overcome this difiiculty the radio oscillations of the incoming signal may be ampligacd and then applie to this protecting detor.

Another method of obtaining nearly an ideal protective characteristic for a vacuum detector is by the introduction of a gas so that a small kink 52 is produced in the plate current curve as shown in Fig. 10 and the resulting curve of sensitiveness S, when plotted, resembles the ideal form of characteristic shown in Fig. 8.

Althoughl have only disclosed one form in which this invention is embodied, it is to be understood that the invention is not limited to any particular construction but might be embodied in various forms without departing from the spirit of the invention or the scope of the appended claims.

Having thus described my invention, I claim and desire to protect by Letters Patent of the United States:

1. In a detector, an evacuated bulb, a tubular plate electrode supported within said bulb, a grid comprising a plurality of convolutions of wire arranged in superposed relation and connected together by a twisted strand wire, said grid being supported with in said electrode out of contact therewith and a filament cooperating with said grid.

2. In a detector, an evacuated bulb a tubular plate electrode supported within said bulb, a grid comprising a plurality of convolutions of wire arranged in superposed relation and connected together by a twisted strand wire arranged in parallel relation to the longitudinal axis of said convolutions, said convolutions passing between the pairs of strands, said grid being supported within said plate electrode out of contact there with and a filament arranged to cooperate with said grid.

3. A vacuum tube grid comprisi a coil of conducting material and twiste strand reinforcin elements extending longitudinally of t e coil.

4. A three electrode vacuum tube including a grid com rising a coil of conducting wire and t strand reinforcing wires arranged longitudinally of the coil and spaced substantiell equal distances, by passing peripherally of the coil. said convo utions between the two interl6 5. A three electrode vacuum tube includwoven strands composing the reenforcing ing a. grid comprising a coil of conducting wires.

5 wire and interwoven two stranded rein- Signed at New York, in the county of forcing wires arranged longitudinally of New York and State of New York, this 24th the coil and connected with the convolutions day of September, A. D. 1918. of the coil to maintain them spaced apart by EMORY LEON OHAFFEE. 

